Short answers, pulled from the story.
Ken Masters first appeared in 1987 as a palette swap of Ryu. This design decision was born from budget constraints rather than creative vision. The character was created to be the American counterpart to Ryu, the Japanese protagonist.
Capcom added the surname Masters to avoid trademark conflict with Mattel's Ken dolls. This full name was later canonized in the animated Street Fighter II movie and the Street Fighter II V series. The name was officially adopted into the video game canon with Street Fighter Alpha 2.
In Street Fighter 6, Ken Masters dropped the red gi entirely to reflect a life that had become less stable. His design changed again to make him more aggressive and dynamic while Ryu was made more defensive and strategic. The character became more aggressive and dynamic, while Ryu was made more defensive and strategic.
Ken Masters married his girlfriend Eliza in the original Street Fighter II ending. Ken and Eliza have a son named Mel who appears as a child in Street Fighter III and a teenager in Street Fighter 6. The narrative of Street Fighter 6 depicts Ken's life unraveling as he learns that his partner JP is a terrorist leader.
David Matranga took over the role of Ken Masters in Street Fighter 6. He noted the challenge of capturing Ken's emotional depth and the need to scream and grunt during attacks. The voice actors have had to adapt to the character's evolving personality from the Alpha series to Street Fighter 6.